A 20 pin connector is the original ATX v1.0 specification for delivering power to the motherboard. A 24 pin connector is part of a newer revision of the ATX specification designed for high performance motherboards (usually dual CPU and higher). The 20+4 is a connector that conforms to the 24 pin specification, but 4 of the pins can actually be "detached" to "convert" it to a 20 pin for older motherboards.

There's a little more to it than that, but that's the basics in a nutshell.

A 20 pin connector is the original ATX v1.0 specification for delivering power to the motherboard. A 24 pin connector is part of a newer revision of the ATX specification designed for high performance motherboards (usually dual CPU and higher). The 20+4 is a connector that conforms to the 24 pin specification, but 4 of the pins can actually be "detached" to "convert" it to a 20 pin for older motherboards.

There's a little more to it than that, but that's the basics in a nutshell.

So if a motherboard specification states that it has a 24 pin connector, then the 20 pin of the power supply would be no-go?

A 20 pin connector is the original ATX v1.0 specification for delivering power to the motherboard. A 24 pin connector is part of a newer revision of the ATX specification designed for high performance motherboards (usually dual CPU and higher). The 20+4 is a connector that conforms to the 24 pin specification, but 4 of the pins can actually be "detached" to "convert" it to a 20 pin for older motherboards.

There's a little more to it than that, but that's the basics in a nutshell.

So if a motherboard specification states that it has a 24 pin connector, then the 20 pin of the power supply would be no-go?

A 20 pin connector is the original ATX v1.0 specification for delivering power to the motherboard. A 24 pin connector is part of a newer revision of the ATX specification designed for high performance motherboards (usually dual CPU and higher). The 20+4 is a connector that conforms to the 24 pin specification, but 4 of the pins can actually be "detached" to "convert" it to a 20 pin for older motherboards.

There's a little more to it than that, but that's the basics in a nutshell.

So if a motherboard specification states that it has a 24 pin connector, then the 20 pin of the power supply would be no-go?

You can always buy a 20 to 24 pin converter, but I would recommend getting an actual 24 pin power supply.

I am new to computer building and have a question: What is the difference between the 20 vs 24 vs 20+4 pin connectors? I am kind of confused... Any explanation would be appreciated.

Yes, definitely get an ATX 2 power supply. Some motherboards are using EPS which is similar but requires an additional 8 pin power cable. Motherboard book or online specs should say what power supply type is requires. The power supply I bought can do both ATX and EPS.

I actually hit the power limit on the first computer I built. It was a 1.4 GHz Athlon Thunderbird and it was a power hungry son-of-a-gun! It ran fine for several months but then one day in the spring I smelled something coming from the area of my computer. It wasn't very strong and at first I didn't think much of it. I was busy with finals and finding a summer job so I ignored it since everything was still working. But later that summer I took the computer apart and found that the ATX 20 pin connector had started to melt. I was eventually able to pry it apart and did some searching through forums and found out that I wasn't the only one to experience this. The 5V rails (used to power the CPU back then) were overheating and melting the plastic around them. Everything still worked... I just couldn't shove enough power though that connector. So I grabbed a soldering iron and soldered the 5V wire from a MOLEX connector to an area on the back of the motherboard where all the 5V rails from the ATX plug ran together in a large area of solder. Worked like a charm for another 2 years.

But this is why they added the "+4" to the original spec. The 4 extra pins carry 12 volts that is now used to power the CPU. More volts = less amps = less loss in transmission = less heat. Often the 4 pins are plugged into the motherboard in a different location than the 20 pin plug - usually right by the CPU. But some boards (I think it is more common in server grade boards) have the 4 pins right next to the 20 pins, essentially making a single 24 pin bock. Hence the difference between "24" and "20+4" but the connectors are small enough that you should be able to plug a "20+4" power supply into a "24" board.

I think all new boards have the 24 pin main power connector, and most also have an additional power connector, this is frequently a 4 pin 12V connector.
But the new motherboard I have just ordered has an 8 pin aux power connector. It can be used with a 4 pin plug from the psu, but it is recommended that an 8 pin plug is used for quad extreme cpu's or if you intend to overclock lower cpu's.

But this is why they added the "+4" to the original spec. The 4 extra pins carry 12 volts that is now used to power the CPU. More volts = less amps = less loss in transmission = less heat. Often the 4 pins are plugged into the motherboard in a different location than the 20 pin plug - usually right by the CPU. But some boards (I think it is more common in server grade boards) have the 4 pins right next to the 20 pins, essentially making a single 24 pin bock. Hence the difference between "24" and "20+4" but the connectors are small enough that you should be able to plug a "20+4" power supply into a "24" board.

That is not correct.

The 4 pin connector you mention is not the same as the 4 pin from a 20+4.

The ATX +4 provide +12V +5V +3.3V and a ground wires in addition to the 20 pins of a standard ATX.
On 24 pins connectors these are the pins labled 11 12 23 24.
This +4 plug wil not fit the 4 pin connector on the motherboard unless you force it which will damge the psu and board beyond repair.

DO NOT EVER DO THIS

Like OzzFan said is the 24 and 20+4 essentialy the same with the added benefit of being backwards compattible with 20 pin boards.
You detach the +4 and tie it somwhere out of the way when using a motherboard with a 20 pin connector.

This leaves the question if you need additional power provided to the board when using a processor with high power requrements.
These are the options